The present invention generally relates to a solid-state imaging device, and more specifically, to a so-called "wide dynamic range CCD solid-state imaging device", the dynamic range of which is wide with respect to a light input.
In CCD solid-state imaging devices, light receiving portions (pixels) are arranged in a two-dimensional matrix form, and photoelectrically converts input light into signal charges, and stores the signal charges. After these signal charges are overflown from the light receiving portions, since the signal outputs based on the overflown signal charges become constant, such a signal output can be hardly obtained which corresponds to incident light amounts exceeding the saturation level of the light receiving portions. As a result, dynamic ranges in response to the light inputs would become narrow.
To extend, or enlarge this narrow dynamic range, there is one conventional solid-state imaging apparatus described in, for instance, Japanese Laid-open Patent Application No. 3-117281. That is, as shown in FIG. 1, two different sorts of light receiving portions having different sensitivities are alternately arranged adjacent to each other. For instance, the high-sensitive light receiving portion 101 and the low-sensitive light receiving portion 102 are alternately arranged adjacent to each other along the vertical direction. The signal charges of the high-sensitive light receiving portion 101 are limited in the light receiving portion and thereafter the limited signal charges are read out from the vertical transfer register 103. After the signal charges of the high-sensitive light receiving portion 101 are mixed with the signal charges of the low-sensitive light receiving portion 102 in this register 103, the mixed signal charges are vertically transferred. Furthermore, the signal charges are horizontally transferred by the horizontal transfer register 104 to the charge detecting portion 105. The horizontally transferred signal charges are converted into the electric signals in this charge detecting portion 105, and thereafter the electric signals are outputted via the buffer 106.
In this CCD solid-state imaging device, when the incident light amount exceeds a predetermined amount, since the limiter is operable to the signal charges of the high-sensitive light receiving portion 101, the signal charges of the high-sensitive light receiving portion 101 are mixed with the signal charges of the low-sensitive light receiving portion 102 to thereby achieve such an input/output characteristic approximated to a bent line shown in FIG. 2. As a result, a wide dynamic range may be realized. It should be noted that in the graphic representation of FIG. 2, a dot and dash line shows the input/output characteristic of the high-sensitive light receiving portion 101, a dotted line indicates the input/output characteristic of the low-sensitive light receiving portion 102, and a solid line represents the input/output characteristic of the mixed signal charges.
However, in the conventional CCD solid-state imaging device with the above-described structure, i.e., the limiters are operated for the respective light receiving portions in the high-sensitive light receiving portion 101, the overflow characteristics are fluctuated in the respective light receiving portions, and since the fluctuations in the saturated charge amounts "Qs" of the respective light receiving portions become large, offsets are produced in the input/output characteristic approximated to the folded line, as shown in FIG. 3. As a result, when a large light amount is entered under which the high-sensitive light receiving portion 101 becomes saturated, there are large fluctuations in the saturated charge amounts "Qs" of the respective light receiving portions. Thus, there is a problem that fixed pattern noise is produced in the images (namely, fluctuation of fixed patterns).